Zeolite composite catalysts for conversion of heavy reformate to xylenes

ABSTRACT

Embodiments of zeolite composite catalysts and methods of producing the zeolite composite catalysts are provided, where the methods comprise dissolving in an alkaline solution a catalyst precursor comprising at least one mesoporous zeolite while heating, stirring, or both to yield a dissolved zeolite solution, where the mesoporous zeolite has a molar ratio of SiO 2 /Al 2 O 3  of at least 30, where the mesoporous zeolite comprises zeolite beta, adjusting the pH of the dissolved zeolite solution, aging the pH adjusted dissolved zeolite solution to yield solid zeolite composite from the dissolved zeolite solution, and calcining the solid zeolite composite to produce the zeolite composite catalyst, where the zeolite composite catalyst has a mesostructure comprising at least one disordered mesophase and at least one ordered mesophase, and where the zeolite composite catalyst has a surface area defined by the Brunauer-Emmett-Teller (BET) analysis of at least 600 m 2 /g.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 15/624,090 filed Jun. 15, 2017, the entire disclosure of whichis hereby incorporated herein by reference.

TECHNICAL FIELD

Embodiments of the present specification generally relate to zeolitecomposite catalysts, and specifically relate to zeolite compositecatalysts and methods of using the same to convert heavy reformate toxylenes.

BACKGROUND

Aromatic hydrocarbon compounds derived from petrochemical sources,benzene (C₆H₆), toluene (methylbenzene, C₇H₈), and xylenes(dimethylbenzenes, C₈H₁₀ isomers) may be used as starting materials fora wide range of consumer products. The xylenes include three isomers ofdimethylbenzene, namely: 1,2-dimethylbenzene (ortho-xylene or o-xylene),1,3-dimethylbenzene (meta-xylene or m-xylene), and 1,4-dimethylbenzene(para-xylene or p-xylene). The three isomers of xylene may be used inthe synthesis of a number of useful products. For example, uponoxidation, the p-xylene isomer yields terephthalic acid, which may beused in the manufacture of polyester plastics and synthetic textilefibers (such as Dacron), films (such as Mylar), and resins (such aspolyethylene terephthalate, used in making plastic bottles). Them-xylene isomer may be used in the manufacture of plasticizers, azodyes, and wood preservers, for example. The o-xylene isomer may be usedas a feedstock for phthalic anhydride production, which in turn may beused to make polyesters, alkyl resins, and PVC plasticizers. Therefore,the demand for xylenes remains strong as markets for polyester fibersand polyethylene terephthalate continue to demonstrate high growthrates.

Environmental regulations in several countries limit the amount ofaromatics that can be blended into the gasoline pool. Most of thearomatics in gasoline originate from catalytic reforming of naphtha.Aromatic hydrocarbon compounds contained in a gasoline generally havehigher octane values and are superior as a gasoline base, because oftheir high calorific values. Among them, toluene and aromatichydrocarbon compounds, especially those having eight carbon atoms, havehigher octane values and drivability levels, thus, it is desirable toincrease the volume of C₈ aromatic compounds in gasoline. Lightreformate of the naphtha is blended into gasoline, because it has a highoctane number and lower boiling point; however, environmentalregulations exclude a substantial quantity of the heavy reformate ingasoline, thus making heavy reformates available for utilizationelsewhere.

Typically, heavy reformate contains 90 weight (wt.) % to 95 wt. % C₉ and5 wt. % to 10 wt. % C₁₀ aromatic compounds. Among the C₉ components,trimethylbenzenes (TMBs) (50 wt. % to 60 wt. %) and methylethylbenzenes(MEBs) (30 wt. % to 40 wt. %) are the major constituents. One of theeconomically viable options is to convert the heavy aromatics in theheavy reformate into valuable products, such as xylenes. Demand isgrowing faster for xylene derivatives than for benzene derivatives.Therefore, a higher yield of xylenes at the expense of benzene yield isa favorable objective.

Heavy reformate can be subjected to transalkylation either alone or withC₇ (toluene) for the production of xylenes (C₈) and benzene (C₆).Because many different compounds may be present in the heavy reformate,multiple parallel and consecutive reactions may take place.Transalkylation reactions for converting aromatic hydrocarbon compoundsto compounds having a different number of carbon atoms may include thedisproportionation reaction of toluene, i.e., two molecules of toluenereact to form one molecule of benzene and one molecule of xylene (bytransfer of a methyl group from one molecule of toluene to the other, atransalkylation reaction). Transalkylation reactions, however, are notlimited to the disproportionation of toluene. Other methods ofincreasing xylene yields operate through inducing transalkylation byadding aromatic hydrocarbon compounds having nine or more carbon atomsinto the starting materials, resulting in such reactions as the additionof one mole of toluene to one mole of a C₉ aromatic hydrocarbon toproduce two moles of xylene. These parallel and consecutive reactionmethodologies may also be accompanied by multiple chemical equilibria,including isomerization of xylenes, TMBs and MEBs. The transalkylationand disproportionation reactions are equilibrium constrained, while thedealkylation reactions are kinetically controlled.

It is also known to separate isomers through molecular sieves formed byzeolites. Zeolites are generally hydrated aluminum and calcium (orsodium) silicates that can be made or selected with a controlledporosity for catalytic cracking in petroleum refineries, and may benatural or synthetic. The pores may form sites for catalytic reactionsto occur, and may also form channels that are selective for the passageof certain isomers to the exclusion of others. Zeolites may serve asBrönsted acids for hydrogen ion exchange by washing with acids, or asLewis acids by heating to eliminate water from the Brönsted sites. Forexample, the zeolite ZSM-5 (Na₃Al₃Si₉₃O₁₉₂.16H₂O) has a pore size thatresults in the formation of channels of such size and shape that itforms a selective sieve for xylene isomers. The alkylation of toluene bymethanol will form a mixture of all three xylene isomers. p-Xylene willpass through the channels in ZSM-5 due to its linear configuration,while o-xylene and m-xylene will not pass through the pores, althoughthey may subsequently rearrange to p-xylene under the acidic conditionsin the pores and then pass through the sieve. The catalytic activity ofzeolites can also be increased by addition of a metal catalyst thatactivates hydrogen by breaking up molecular hydrogen to atomic hydrogenon the surface of the metal for forming intermediates in transalkylationreactions.

Regardless, these conventional means to produce xylenes by fractionationof reformate results in a xylene yield that is insufficient to meet thedemand, and conversion of other hydrocarbons is necessary to increasethe yield of xylenes. Furthermore, xylene isomer streams from catalyticreforming or other sources do not meet the demand as chemicalintermediates. Para-xylene in particular is a major chemicalintermediate with rapidly growing demand, but equates to only 20% to 25%of a typical C₈ aromatics stream.

SUMMARY

Accordingly, ongoing needs exist for catalysts suitable for convertingheavy reformates to produce xylenes. Embodiments of the presentdisclosure are related to zeolite composite transalkylation catalysts,their preparation methods and performance, particularly to the synthesisof such catalysts having an ordered/disordered mesostructure andhydrothermal stability. The zeolite composite catalysts may convert amixture of heavy aromatic compounds, particularly C₉ aromatichydrocarbons to benzene, toluene, and xylenes, and particularly tocommercially valuable xylenes. The conversion reactions includedealkylation, transalkylation, disproportionation and isomerization. Thezeolite composite catalysts have a high ethyl-dealkylation activity aswell as high methyl-transalkylation activity to improve the yield ofxylenes.

According to one embodiment, a method of producing a zeolite compositecatalyst is provided. The method comprises dissolving in an alkalinesolution a catalyst precursor comprising mesoporous zeolite whileheating, stirring, or both to yield a dissolved zeolite solution, wherethe mesoporous zeolite has a molar ratio of SiO₂/Al₂O₃ of at least 30,where the mesoporous zeolite comprises zeolite beta, adjusting the pH ofthe dissolved zeolite solution, aging the pH adjusted dissolved zeolitesolution to yield solid zeolite composite from the dissolved zeolitesolution, and calcining the solid zeolite composite to produce thezeolite composite catalyst, where the zeolite composite catalyst has amesostructure comprising at least one disordered mesophase and at leastone ordered mesophase, and where the zeolite composite catalyst has asurface area defined by a Brunauer-Emmett-Teller (BET) analysis of atleast 600 m²/g.

According to another embodiment, a zeolite composite catalyst isprovided. The zeolite composite catalyst comprises a mesostructurecomprising at least one disordered mesophase and at least one orderedmesophase, where the zeolite composite catalyst has a surface areadefined by the Brunauer-Emmett-Teller (BET) analysis of at least 600m²/g and where the zeolite composite catalyst comprises zeolite beta.

According to yet another embodiment, a method of converting C₉₊ alkylaromatic hydrocarbons to a product stream comprising benzene, toluene,and xylene is provided. The method comprises reducing a zeolitecomposite catalyst comprising a mesostructure comprising at least onedisordered mesophase and at least one ordered mesophase, where thezeolite composite catalyst has a surface area defined by BET of at least600 m²/g with hydrogen gas at 400° C., where the zeolite compositecatalyst comprises zeolite beta. The method further comprisingcontacting a feed comprising C₉₊ alkylaromatic hydrocarbons with thereduced composite zeolite catalyst and hydrogen in a transalkylationzone of a reactor to produce a transalkylation product, stripping C₁-C₅and lighter hydrocarbons and stripping unreacted feed from thetransalkylation product, and collecting xylenes product from thetransalkylation product.

Additional features and advantages of the described embodiments will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the described embodiments, including thedetailed description which follows, the claims, as well as the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart depicting the synthesis of a zeolite compositecatalyst in accordance with one or more embodiments of the presentdisclosure.

FIG. 2 is a schematic illustration depicting the conversion of heavyreformate into xylenes in accordance with one or more embodiments of thepresent disclosure.

FIG. 3 is an X-Ray Diffraction (XRD) graph of a zeolite compositecatalyst with an ordered hexagonal mesophase, which was produced throughdissolution of zeolite beta using 0.45 Molarity (M) NaOH solution in thepresence of cetyl trimethyl ammonium bromide (CTAB).

FIG. 4 is an XRD graph of a zeolite composite catalyst having an orderedhexagonal mesophase and a disordered hexagonal mesophase, which wasproduced through the dissolution of zeolite beta using 0.1 M NaOHsolution in the presence of CTAB in accordance with one or moreembodiments of the present disclosure.

FIG. 5 is an XRD graph of a zeolite composite catalyst having an orderedhexagonal mesophase and a disordered hexagonal mesophase, which wasproduced through the dissolution of zeolite beta using 0.2 M NaOHsolution in the presence of CTAB in accordance with one or moreembodiments of the present disclosure.

FIG. 6 is a graph illustrating the pore size distribution of thecatalyst depicted in FIG. 3.

FIG. 7 is a graph illustrating the pore size distribution of thecatalyst depicted in FIG. 4 in accordance with one or more embodimentsof the present disclosure.

FIG. 8 is a graph illustrating the pore size distribution of thecatalyst depicted in FIG. 5 in accordance with one or more embodimentsof the present disclosure.

FIG. 9 is a TEM image showing ordered hexagonal phase and disorderedhexagonal phase in accordance with one or more embodiments of thepresent disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of a zeolitecomposite catalyst comprising a mesostructure comprising at least onedisordered mesophase and at least one ordered mesophase. In oneembodiment, the ordered mesophase is a hexagonal mesophase, and thedisordered mesophase comprises a hexagonal mesophase. Without beingbound by theory, composite catalyst with ordered and disorderedmesophase formation provides improved transalkylation catalyst activity,which provides improved yield of xylenes as compared to zeolite beta andor typical zeolite beta/MCM-41 composite zeolites. As defined, “orderedmesophase” means a crystalline zeolite uniform arrangement of mesopores,where “mesopores” have an average pore diameter between 2 and 50nanometers. As defined, “disordered mesophase” means a non-uniformarrangement of pores, where mesopores have an average pore diameterbetween 2 and 50 nanometers. As defined, “ordered/disordered phase”means the surface has a combination of at least one ordered mesophaseand at least one disordered mesophase as shown in the transmissionelectron microscopy (TEM) image of FIG. 9.

In one embodiment, the zeolite composite catalyst may comprise asilica-alumina compound. In another embodiment, the silica-aluminacompound may comprise a molar ratio of SiO₂/Al₂O₃ of at least 30.Moreover, the molar ratio of SiO₂/Al₂O₃ may be from 30 to 100, or from40 to 80.

In one embodiment, the zeolite composite catalyst may comprise zeolitebeta. Zeolite beta is a complex intergrowth family, whose desilicationstability is lower than ZSM-5 and mordenite. A commercial embodiment ofthe zeolite beta is HSZ-940NHA, available from Tosoh Corporation, Japan.In addition, the mesoporous zeolite of the catalyst precursor maycomprise at least additional metal or metal oxide in the framework ormatrix of the zeolite catalyst. The additional metal or metal oxide inthe framework of the zeolite composite catalyst may include zirconium,germanium, tin, or combinations thereof. While various amounts areconsidered suitable, the molar ratio of silica to the additional metalcomponents (e.g., germanium, zirconium, tin, or combinations thereof)may be from 5 to 100, or from 20 to 100.

Moreover, the zeolite composite catalyst may also comprise at least oneadditional zeolite, for example, medium or large pore zeolites selectedfrom the group of mordenite, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, MFItopology zeolite, NES topology zeolite, EU-1, MAPO-36, SAPO-5, SAPO-11,SAPO-34, and SAPO-41. For purposes of this disclosure small porezeolites have a pore size of 3-5 angstroms (Å), medium pore zeoliteshave a pore size of 5-6 Å, and large pore zeolites have a pore size of6-8 Å. Without being limited to theory, this may allow the zeolitecomposite catalyst to maintain the acidity advantage of the medium orlarge pore zeolite while inheriting pore structure qualities of themesoporous materials. The amount of this second zeolite may range from10 to 90 wt % of the total zeolite composite catalyst amount in thefinal dried and calcined form. The acidity is defined by the ratio ofsilica to alumina groups in the particular zeolite composite catalyst.The zeolite composite catalyst has an intermediate acidity. For purposesof this disclosure a silica to alumina ratio less than 20 is consideredhigh acidity, a silica to alumina ration in the range of 30 to 100 isconsidered an intermediate acidity, and a silica to alumina ratio ofmore than 100 is considered a low acidity.

Moreover, the zeolite composite catalysts may be impregnated with activemetals for catalysis, for example, active metals selected from the groupconsisting of molybdenum, chromium, platinum, nickel, platinum,palladium, or combinations thereof. In one embodiment, the active metalis molybdenum. The metal component may exist within the final catalyticcomposite as a compound, such as an oxide, sulfide or halide, inchemical combination with one or more of the other ingredients of thecomposite, or as an elemental metal. The active metal component may bepresent in the final zeolite composite catalyst in any amount that iscatalytically effective, generally comprising 0.01 to 5 wt % of thefinal catalyst calculated on an elemental basis.

As described in the synthesis discussion as follows, the zeolitecomposite catalyst may include a zeolite beta/MCM-41 structure producedfrom a zeolite beta precursor. In at least one embodiment, the zeolitecomposite catalyst comprises less than 20% of MCM-41 mesoporous contentformed from the zeolite beta precursor.

From a property standpoint, the zeolite composite catalyst may have asurface area defined by a Brunauer-Emmett-Teller (BET) analysis of atleast 600 meters²/g (m²/g), or a BET surface area of at least 700 m²/g.Further, the zeolite composite catalyst may have an external surfacearea of at least 300 m²/g, or an external surface area of at least 350m²/g.

In one or more embodiments, the zeolite composite catalyst may have atotal pore volume of 0.20 to 3.0 cm³/g, or 0.30 to 1.0 cm³/g. Moreover,the zeolite composite catalyst may have a total pore volume of at least0.30 cm³/g, or of at least 0.40 cm³/g, or at least 0.50 cm³/g. Inanother embodiment, the zeolite composite catalyst may have an averagepore diameter of at least 30 angstroms (3 nanometers).

Referring to FIG. 1, the method of producing the zeolite compositecatalyst may comprise the steps of providing a catalyst precursor 10comprising a mesoporous zeolite having a molar ratio of SiO₂/Al₂O₃ of atleast 30 and dissolving in an alkaline solution while heating, stirring,or both to yield a dissolved zeolite solution 20. In one embodiment, thecatalyst precursor comprises zeolite beta to yield the zeolite betaprecursor. Additionally, the catalyst precursor may comprise zeolitebeta and at least one additional mesoporous zeolite selected from thegroup consisting of mordenite, ZSM-22, ZSM-12, and combinations thereofto yield an alternate zeolite beta precursor.

The dissolving step, also called desilication, may be conducted in thepresence of a surfactant 30, where the surfactant is often called atemplating agent for the zeolite catalyst. While the FIG. 1 embodimentshows templating surfactant, it is contemplated in other embodimentsthat surfactant is absent. For example and not by way of limitation, thesurfactant is a cationic surfactant. The cationic surfactant may includea quaternary ammonium compound. For example and not by way oflimitation, the quaternary ammonium cationic surfactant may becetyltrimethyl ammonium bromide (CTAB). Various amounts of surfactantare contemplated for inclusion in the catalyst precursor. For example,the catalyst precursor may include 1 weight % to 10 weight % surfactant,for example CTAB, or 2 weight % to 8 weight % surfactant, for exampleCTAB.

During conventional desilication, the mesoporosity in the zeolite isgenerated by desilication using standard conditions. For example,desilication may be performed using 0.2 M NaOH with 30 min of stirringat 65° C. By this process, one third of catalyst is lost due todesilication; however, the present method utilizes that desilicatedsource to generate mesoporosity using the surfactant template.

Further as shown in FIG. 1, the dissolution may occur slowly in thepresence of a surfactant template by gradual heating for 24 hours. Byanother method, the desilication can also take place in the absence of asurfactant template. In one embodiment, the desilication may occur inthe absence of a surfactant template by stirring for 30 minutes. Thefiltrate is collected and mesopores are generated using a templatemediated technique. In this way, the wasted desilicated source isutilized to produce the mesophases. Various heating processes orelements are contemplated. For example, the heating may be hydrothermalheating. In one or more embodiment, the hydrothermal heating may occurat a temperature of 50 to 150° C., or a temperature of 90 to 110° C.Furthermore, the duration of hydrothermal heating may range from 30minutes to 24 hours.

Various alkaline solutions are contemplated for the desilication. In oneembodiment, the alkaline solution may comprise NaOH. In specificembodiments, the alkaline solution may comprise 0.01 to 0.2 Molarity (M)NaOH, 0.05 to 0.2 Molarity (M) NaOH, or 0.05 to 0.1 M NaOH. Withoutbeing bound by theory, it is surprisingly discovered that controllingthe molarity of the NaOH is a parameter that impacts theordered/disordered phase mesostructure of the zeolite compositecatalyst.

Referring again to FIG. 1, the method may comprise the step 40 ofadjusting the pH of the dissolved zeolite solution. The adjusting of thepH is performed by an acidic solution. Various acids are contemplated.In one embodiment, the acidic solution comprises sulfuric acid. In oneembodiment the pH is adjusted to 8 to 10.

Next, various additional steps 50 may be utilized, for example,hydrothermal aging, filtering, washed drying, ion-exchanging andcalcining the pH adjusted dissolved zeolite solution. The hydrothermalaging may involve maintaining the pH adjusted dissolved zeolite solutionat a temperature of 75 to 125° C. for a duration of 12 to 48 hours.During hydrothermal aging, the soluble aluminosilicate species arehydrothermally condensed to form mesophases. The ion exchange may occurin the presence of a nitrate solution, for example and not by way oflimitation, a solution comprising NH₄NO₃. Moreover, it is contemplatedthat the zeolite may be steamed at 600-750° C. for 4 hours. At thisstage 60, the solid composite zeolite with ordered/disordered mesophaseis formed.

Referring to FIG. 1, the process may also include the step 70 ofextruding the solid zeolite composite in the presence of binder. Arefractory binder or matrix is optionally utilized to facilitatefabrication of the catalyst, to provide strength, and to reducefabrication costs. Suitable binders include inorganic oxides, such asone or more of alumina, magnesia, zirconia, chromia, titania, boric,phosphate, zinc oxide and silica. In one embodiment, the binder is analumina based binder. One commercial embodiment of the alumina binder isCataloid AP-3, obtained from Catalysts & Chemicals Industries Co., Ltd(CCIC), Japan. The zeolites may be mixed in dry powdered form with thealumina binder in aqueous form to yield a homogeneous mixture, thusensuring homogeneous composition of the extrudates formed. In one ormore embodiments, the ratio by weight of solid zeolite composite tobinder is 4 to 1, or 3 to 1. The extrusion with binder step 70 may beconducted at a temperature of 100 to 150° C. for a duration of 30minutes to 2 hours.

Next, the process may comprise the step 70 of impregnating solid zeolitecomposite with one or more active metals prior to a calcining step. Theone or more active metals are selected from the group consisting ofmolybdenum (Mo), platinum (Pt), rhenium (Re), nickel (Ni), andcombinations thereof. In one embodiment, the active metal may comprise 2to 6% by weight molybdenum. Optionally, the zeolite composite may bedried after wet impregnation for at least 2 hours at 100° C.

Referring again to FIG. 1, another calcining step 90 may be utilized toproduce the zeolite composite catalyst, which is effective as atransalkylation catalyst 100. The calcining step may occur for 4 to 8hours at a temperature of 400 to 500° C., or for 4 hours at atemperature of 400° C.

Further as stated above, the present zeolite composite catalyst is atransalkylation catalyst suitable for converting C₉₊ alkyl aromatichydrocarbons to a product stream comprising benzene, toluene, andxylene, particularly to commercially valuable xylenes. The feed streamto the conversion process generally comprises alkylaromatic hydrocarbonsin the carbon number range C₉ to C₁₁₊ that may include, for example,such hydrocarbons as propylbenzenes, ethylmethylbenzenes,tetramethylbenzenes, ethyldimethylbenzenes, diethylbenzenes,methylpropylbenzenes, and mixtures thereof. The heavy aromatics feedstream, characterized mainly by C₉₊ aromatics, permits effectivetransalkylation of light aromatics such as benzene and toluene with theheavier C₉₊ aromatics to yield additional C₈ aromatics, such as xylenes.The heavy aromatics stream preferably comprises at least 90 wt. % C₉aromatics, and may be derived from the same or different known refineryand petrochemical processes, and may be recycled from the separation ofthe product from transalkylation.

Referring to the embodiment of FIG. 2, the method of using the zeolitecomposite catalyst as a transalkylation catalyst may optionally includeheating a feed 110 comprising C₉₊ alkylaromatic hydrocarbons from a feedsource 105 with a heater unit 111. As shown, the heater unit 111 may bea heat exchanger which receives a heated stream 108, for example, aheated water stream to heat the feed 110 prior to delivery to thereactor system 113. Other methods of heating the feed are contemplated.

The reactor system may include a single reactor 113 with zeolitecomposite catalyst used in transalkylation catalyst zone 115 as shown inFIG. 2, or may include multiple reactors or stages. The reactor 113 isdepicted as a downflow 114 reactor but that is one of manypossibilities. In the embodiment of FIG. 2, the reactor 113 has a fixedcylindrical bed of catalyst; however, other reaction configurationsutilizing moving beds of catalyst or radial-flow reactors or fluidizedbed may be employed. Prior to the feed being delivered, the zeolitecomposite catalyst in transalkylation catalyst zone 115 may be reduced,for example, reduced with hydrogen gas 112. In one embodiment, thezeolite composite catalyst is reduced by hydrogen gas 112 at atemperature of 350 to 450° C., or 400° C.

Referring again to FIG. 2, the feed stream 110 contacts the reducedcomposite zeolite catalyst and hydrogen 112 in the transalkylationcatalyst zone 115 of the reactor 113. Specifically, the feed 110 istransalkylated in the vapor phase and in the presence of hydrogen 112.The hydrogen 112 may be delivered with the feed stream 110 in an amountfrom 0.1 to 10 moles of hydrogen per mole of alkylaromatics. This ratioof hydrogen to alkylaromatics is also referred to as thehydrogen-to-hydrocarbon ratio. The transalkylation results in theproduction of a transalkylation effluent stream 116 comprising producthydrocarbons, specifically, hydrocarbons having mixed xylene content, aswell as unconverted feed, toluene, and benzene. Various conditions arecontemplated for the reactor 113. Specifically, the transalkylationcatalyst zone 115 may include a temperature between 200° C. and 540° C.and moderately elevated pressures of 1.0 MPa to 5.0 MPa. The liquidhourly space velocity (LHSV) is in the range of 1.0 hr⁻¹ to 5.0 hr⁻¹.

As shown, the transalkylation effluent stream 116 may be cooled using acooler 117. The cooler 117 may be a heat exchanger, condenser, or anyother suitable cooling device familiar to the skilled person. As shown,the cooler 117 is a heat exchanger which includes a cooling stream 118.Next, the transalkylation effluent stream 116 may be fed to a strippercolumn 120, where C₁-C₅ and lighter hydrocarbons 122 are separated fromthe transalkylation effluent stream 116. Additionally, unreacted feedmay be stripped from the transalkylation effluent stream 116.

Referring to FIG. 2, the product 124 of the stripper column 120, whichmay be discharged from the bottom of the stripper column 120, mayinclude a light recycle stream comprising benzene and toluene, a mixedC₈ aromatics product, and a heavy recycle stream. These all maysubsequently be separated in one or more reaction vessels 125, 127, 129.The mixed C₈ aromatics product 128 can be sent for recovery of p-xylene132 and other valuable isomers 134. The light recycle stream 126 mayundergo benzene and toluene recovery 136 with a portion recycled to thetransalkylation zone or the feed source 105. The heavy recycle stream130 may contain substantially all of the C₉ and heavier aromatics andmay be partially or totally recycled to the transalkylation reactionzone, or delivered to the feed source 105 for recycle, or removed fromthe process for disposal or other processing.

EXAMPLES

The described embodiments will be further clarified by the followingexamples.

For demonstration purposes, the preparation of composite catalysts isprovided as follows. The synthesis of Catalyst A, which includes anordered hexagonal phase, is described in Example 1. The preparation ofcomposite Catalyst B with disordered hexagonal mesophase is described inExample 2. The preparation of composite Catalyst C withordered/disordered hexagonal mesophase is presented in Example 3. Theperformance of Catalyst A was compared with a physical mixture of twozeolites which are constituents of Catalyst A in Example 4. Theperformance of Catalyst A was compared with one of its constituents(zeolite beta) in Example 5. Example 6 described the preparation ofdesilicated zeolite beta 40 (Catalyst D). Preparation of metal-loadedcomposite catalysts (A-1, B-1, C-1, E-1, F-1 and G-1), is described inExample 7. The performance of Catalysts A-1, B-1, C-1, D, E-1, F-1 andG-1 is compared in Example 8. Finally, Example 9 describes thepreparation of mesoporous zeolite beta composite catalyst usingdesilicated filtrate solution.

The catalysts described in these examples are exemplary embodimentsonly, and are not intended to limit the general description of thecomposite catalyst covering this invention. In each example, the zeolitebeta is HSZ-940NHA, available from Tosoh Corporation, Japan.

Example 1: Preparation of Hierarchical Catalyst A with Ordered HexagonalMesophase

Two grams of zeolite beta (Si/Al molar ratio=40) was disintegrated using0.45 M NaOH solution by gradual heating (without stirring) at 100° C.for 24 hours (h). The heating was carried out in the presence of CTAB(4.45 wt. %). The mixture was cooled down and then the pH was adjustedto 9.0 through the addition of dilute sulfuric acid (2 Normality (N)equivalents/liter). The mixture was then stirred for 24 hours (h) andthen aged at 100° C. for 24 h to form a zeolite beta/MCM-41 composite.The solid product was filtered, washed thoroughly using distilled water,dried at 80° C. overnight, then calcined at 550° C. for 6 h to removethe surfactant. The composite material thus obtained was ion-exchangedthree times with 0.05 M NH₄NO₃ solution at 80° C. for 2 h then calcinedat 550° C. for 2 h. The resulting zeolite beta/MCM-41 composite isdesignated as Catalyst A.

As shown in FIG. 3, the dissolution of zeolite beta using 0.45 M NaOHsolution in the presence of CTAB leads to the formation of Catalyst A, atypical biporous composite with ordered hexagonal mesophase. In the lowX-ray diffraction angle, an intense peak indexed at (100) along withintense higher order diffraction peaks indexed at (110) and (200),corresponding to MCM-41, were observed.

Example 2: Preparation of Composite Catalyst B with Ordered/DisorderedHexagonal Mesophase

Two grams of zeolite beta (Si/Al ratio=40) was disintegrated using 0.1 MNaOH solution by gradual heating (without stirring) at 100° C. for 24 h.The heating was carried out in the presence of CTAB (4.45 wt. %). Themixture was cooled down and then the pH was adjusted to 9.0 through theaddition of dilute sulfuric acid (2N). The mixture was then stirred for24 h and then aged at 100° C. for 24 h to form a zeolite beta/MCM-41composite. The solid product was filtered, washed thoroughly usingdistilled water, dried at 80° C. overnight, then calcined at 550° C. for6 h to remove the surfactant. The composite material thus obtained wasion-exchanged three times with 0.05 M NH₄NO₃ solution at 80° C. for 2 hthen calcined at 550° C. for 2 h. The resulting zeolite beta/MCM-41composite is designated as Catalyst B.

The dissolution of zeolite beta using 0.1 M NaOH solution in thepresence of CTAB leads to the formation of mesopores with disorderedhexagonal mesophase as shown in FIG. 4. The XRD pattern indicates theformation of mesoporous zeolite beta containing highly zeolite betacharacter along with a disordered hexagonal mesophase.

Example 3: Preparation of Composite Catalyst C with Ordered/DisorderedHexagonal Mesophase

Two grams of zeolite beta (Si/Al ratio=40) was disintegrated using 0.2 MNaOH solution by gradual heating (without stirring) at 100° C. for 24 h.The heating was carried out in the presence of CTAB (4.45 wt. %). Themixture was cooled down and then the pH was adjusted to 9.0 through theaddition of dilute sulfuric acid (2N). The mixture was then stirred for24 h and then aged at 100° C. for 24 h to form a zeolite beta/MCM-41composite. The solid product was filtered, washed thoroughly usingdistilled water, dried at 80° C. overnight, then calcined at 550° C. for6 h to remove the surfactant. The composite material thus obtained wasion-exchanged three times with 0.05 M NH₄NO₃ solution at 80° C. for 2 hthen calcined at 550° C. for 2 h. The resulting zeolite beta/MCM-41composite is designated as Catalyst C. Table 1 includes selectedproperties of Catalyst C.

TABLE 1 Catalyst C Data BET External Average Total t-plot SurfaceSurface Pore Pore Micropore Area Area Diameter Volume Volume Catalyst(m²/g) (m²/g) (Å) (cm³/g) (cm³/g) Zeolite 714 388 33.47 0.59 0.16Beta/MCM-41 (Catalyst C)

As shown in FIG. 5, the dissolution of zeolite beta using 0.2 M NaOHsolution in the presence of CTAB leads to the formation of a lessintense hexagonal phase containing ordered/disordered mesophase.

Referring to FIGS. 6-8, catalyst A exhibits narrow mesopore sizedistribution (FIG. 6). However, the pore size distribution of disorderedmesophase containing Catalyst B (FIG. 7) and the ordered/disorderedmesophase Catalyst C shows that the pores are not uniformly distributed(FIG. 8) as compared to typical biporous composite.

Example 4: Comparison of Catalyst A with Physical Mixture of itsConstituents

The activity of Catalyst A for transalkylation reaction was tested in abench top reaction system using a feedstock containing 1,2,4-trimethylbenzene and toluene in a 1:1 molar ratio. A catalyst made by physicallymixing zeolite beta and MCM-41 in equal proportion (Catalyst PMBM) wasalso tested in order to demonstrate effectiveness of the compositecatalyst for C₉ conversion and xylene yield. The catalytic testconsisted of loading a vertical reactor with 2.0 milliliters (ml) of thecatalyst in the middle of the reactor together with inert alumina ballsin the lower and upper parts of the reactor. The total volume of thereactor was 5 ml. The catalyst was activated and reduced under a 50ml/min flow of pure hydrogen gas at 400° C. and was kept at thistemperature for 2 hours. Then, the pressure of the reactor was increasedto 20 bar and the flow of feedstock was started at 4.8 ml/h. Thereaction was allowed to run 3 hours at this temperature beforecollecting the product sample.

The reaction product was directly injected into an on-line gaschromatograph equipped with a flame ionization detector. The hydrocarbonseparation was carried out on a 50 meter (m) long and 0.15 millimeters(mm) diameter column under temperature programmed conditions. Thecomponents were separated according to their boiling points. Thecomponents were identified using a calibration that was accomplishedusing a standard hydrocarbon mixture sample having components of a knowncomposition. The composition of the gaseous product was analyzedoff-line by a gas chromatograph equipped with a flame ionizationdetector and thermal conductivity detector. The gaseous hydrocarbons andhydrogen were analyzed by a 50 m long capillary column.

From the data shown in Table 2 as follows, Catalyst A shows asubstantially higher yield of xylenes as compared to the physicalmixture of zeolite beta and MCM-41 (Catalyst PMBM) under identicalprocess conditions. These results indicate that the composite catalystcontaining zeolite beta and MCM-41 possesses a unique structure whichperforms differently from a mere mixture of its constituents.

TABLE 2 Performance Comparison of Catalyst A with Physical Mixture ofits Constituents Catalyst Product Analysis A PMBM Alkanes 0.66 1.57Benzene 5.58 2.85 Toluene 39.48 20.08 EB 0.33 0.00 p-Xylene 9.35 6.27m-Xylene 20.86 13.75 o-Xylene 9.09 6.23 135-TMB 3.66 8.69 124-TMB 8.7423.59 123-TMB 1.24 4.02 1245-TeMB 0.39 4.85 1235-TeMB 0.51 6.451234-TeMB 0.11 1.65 124-TMB Conversion (wt. %) 84.1 57.1 Xylenes Yield(wt. %) 39.3 26.3

Example 5: Comparison of Catalyst A with Zeolite Beta

The activity of Catalyst A for transalkylation reaction was tested in abench top reactor using industrial heavy reformate feedstock. A sampleof zeolite beta was also tested in order to demonstrate effectiveness ofthe composite catalyst for C₉ conversion and xylene yield. The procedureused for determination of catalytic activity was same as described inExample 4, expect for the feedstock which was industrial heavy reformatefeedstock. The composition of the heavy reformate is presented in Table3.

TABLE 3 Heavy Reformate Composition Major Hydrocarbons Amount (wt. %)Isopropyl benzene 1.8 n-Propyl-benzene 4.4 1-Methyl, 3-ethyl benzene18.5 1-Methyl, 4-ethyl benzene 9.1 1,3,5-trimethyl benzene 10.11-Methyl, 2-ethyl benzene 6.5 1,2,4-trimethyl benzene 39.11,2,3-trimethyl benzene 6.6 Total C₉ Components 96.1 Total C₁₀Components 3.9

From the product compositional data shown in Table 4, Catalyst Aprovided higher yield of xylenes compared to zeolite beta. The data alsoshows higher percent conversion of individual C₉ hydrocarbons,especially the major ones listed in Table 3.

TABLE 4 Performance Comparison of Catalyst A with Zeolite Beta CatalystProduct Analysis Zeolite Beta A Light Alkanes 1.69 1.63 Benzene 1.011.75 Toluene 9.00 12.99 EB 2.39 2.50 p-Xylene 5.17 7.13 m-Xylene 11.1315.72 o-Xylene 4.81 6.75 135 TMB 11.35 8.63 124 TMB 24.37 18.89 123 TMB3.14 2.34 1M2EB 1.60 1.29 1M3EB 2.76 2.19 1M4EB 7.04 5.63 1245 TeMB 2.741.95 1235 TeMB 2.99 2.27 1234 TeMB 0.68 0.45 DEBs 4.27 5.70 Other C10+3.85 2.19 C₉+ Conversion (wt. %) 56.8 66.7 Xylenes Yield (wt. %) 21.129.6

Example 6—Preparation of Desilicated Zeolite Beta 40 (Catalyst D)

Two grams of zeolite beta (Si/Al molar ratio=40) was desilicated using0.2 M NaOH solution by stirring at 65° C. for 30 min. The mixture wascooled down and the solid product was filtered, washed thoroughly usingdistilled water, and dried at 80° C. overnight. The material thusobtained was ion-exchanged three times with 0.05-M NH₄NO₃ solution at80° C. for 2 h then calcined at 550° C. for 2 h. The resultingdesilicated zeolite is designated as Catalyst D.

Example 7—Preparation of Metal-Loaded (Pt, Mo) Composite Catalysts

From the Examples 1-3, the composite catalyst A was found to be activefor transalkylation. In order to improve the performance, the catalystswith hexagonally ordered and disordered pore-structures were preparedand active metal(s) were loaded on composite Catalysts A, B and C.

Examples of such molybdenum-loaded composite catalysts are designated asCatalyst A-1 (4.0 wt. % Mo), B-1 (4.0 wt. % Mo), and C-1 (4.0 wt. % Mo).The activity was compared with conventional desilicated Zeolite Beta 40(Catalyst D). A catalyst loaded with platinum on Catalyst A isdesignated as Catalyst E-1 (2.0 wt. % Pt). A catalyst loaded withmolybdenum on Catalyst A is designated as Catalyst F-1 (2.0 wt. % Mo). Acatalyst loaded with platinum and molybdenum on Catalyst A is designatedas Catalyst G-1 (1.5 wt. % Mo+0.5 wt. % Pt). The incipient wetnessimpregnation method was applied for metal-loading and its procedure issummarized as follows:

Step 1: One gram of catalyst A was soaked in 1.72 grams (g) of deionizedwater for pore volume saturation; Step 2: 0.0397 g of tetraamineplatinum nitrate was dissolved in 1.72 g of deionized water; Step 3: Onegram of catalyst A was then added and homogeneously mixed with adissolved platinum or molybdenum solution; and Step 4: The sample wasdried overnight at 100° C. followed by calcination at 400° C. for fourhours (heating rate was 5° C./min).

In case of bimetallic impregnation, initially 1.5 wt. % Mo wasimpregnated, dried and then 0.5 wt. % Pt was impregnated. Then thesample was calcined at 400° C. for four hours. The heating rate was 5°C./min.

Example 8—Performance Comparison of Metal-Loaded Catalysts A-1, B-1,C-1, E-1, F-1 and G-1 with Desilicated Catalyst D

The activity of catalysts for transalkylation reaction was tested in abench top reaction system using industrial heavy reformate feedstock.The procedure used for determination of catalytic activity was the sameas described in Example 4.

From the product compositional data shown in Table 5 it can be noticedthat impregnation of active metal(s) resulted in significantimprovement, especially in selectivity towards xylenes. The compositionof product obtained over 2% Mo (Catalyst F-1) shows marked reduction inlight hydrocarbon yield. It also shows higher TMB conversion and thusimproved xylene yield (29.5 wt. %).

TABLE 5 Performance Comparison of Metal-Loaded Catalysts A-1, B-1, C-1,E-1, F-1 and G-1 with desilicated Catalyst D Catalyst Catalyst CatalystCatalyst Catalyst Catalyst Catalyst D A-1 B-1 C-1 E-1 F-1 G-1 ProductComposition (wt. %) Light Hydrocarbons 7.00 1.63 2.95 2.14 12.76 1.045.89 Benzene 1.07 1.75 1.02 1.31 0.83 1.13 1.01 Toluene 9.83 12.99 10.8013.56 8.34 11.01 8.68 Ethylbenzene 1.54 2.50 1.25 0.78 0.72 1.54 0.66p-xylene 4.97 7.13 6.25 6.71 4.91 6.27 6.19 m-xylene 15.35 15.72 16.8619.34 14.57 16.66 15.64 o-xylene 5.93 6.75 7.02 7.64 5.69 6.54 6.331-Methyl-2-ethylbenzene 0.65 1.29 1.04 1.50 0.86 0.39 0.881-Methyl-3-ethylbenzene 4.20 2.19 3.32 1.79 3.15 3.70 1.901-Methyl-4-ethylbenzene 1.88 5.63 1.88 1.02 1.42 2.10 1.071,2,3-Trimethylbenzene 3.12 2.34 2.75 2.85 3.30 1.66 2.931,2,4-Trimethylbenzene 21.64 18.89 20.37 20.82 23.30 21.01 21.981,3,5-Trimethylbenzene 9.05 8.63 8.14 7.43 9.25 7.58 7.921,2-Diethylbenzene 2.54 3.10 0.63 0.90 0.00 1.01 0.96 1,3-Diethylbenzene2.50 2.60 2.23 1.29 0.00 0.22 0.61 1,2,3,4-Tetramethylbenzene 0.98 0.451.10 1.11 0.90 0.26 1.28 1,2,3,5-Tetramethylbenzene 4.02 2.27 4.93 4.583.81 4.83 5.71 1,2,4,5-Tetramethylbenzene 1.20 2.74 2.98 2.77 2.91 2.963.43 Others (C₁₀+ aromatics) 2.53 2.19 4.49 2.46 3.27 10.09 6.93Conversion (wt. %) Trimethylbenzenes 45.88 49.96 50.22 45.88 35.75 45.7941.16 Methylethylbenzenes 76.62 78.32 85.03 76.62 84.06 81.85 88.71 C₉+45.69 46.14 51.48 45.69 47.83 44.19 44.40 Xylenes Yield (wt. %) 26.2530.14 33.69 26.25 25.18 29.47 28.16 Xylenes Selectivity (%) 57.45 65.3265.44 57.45 52.64 66.69 63.42

Example 9: Preparation of Mesoporous Zeolite Beta Composite CatalystUsing Desilicated Filtrate Solution

Zeolite beta was desilicated by stirring with 60 mL of 0.2 M NaOHsolution at 65° C. for 30 min. The solid product was filtered, washedthoroughly using distilled water, dried and ion-exchanged and calcinedat 500° C. for 2 h.

The filtrate was collected and used for mesostructure transformation, inthe presence of CTAB (2-8 wt. %). The mixture was cooled down and thenthe pH of the mixture was adjusted to 9.0 through the addition of dilutesulfuric acid (2N). The mixture was then stirred for 24 h and then agedat 100° C. for 24 h to form a hierarchical zeolite beta. The solidproduct was filtered, washed thoroughly using distilled water, dried at80° C. overnight, then calcined at 550° C. for 6 h to remove thesurfactant. The composite material thus obtained was ion-exchanged threetimes with 0.05 M NH₄NO₃ solution at 80° C. for 2 h then calcined at550° C. for 2 h.

It should be apparent to those skilled in the art that variousmodifications and variations can be made to the described embodimentswithout departing from the spirit and scope of the claimed subjectmatter. Thus, it is intended that the specification cover themodifications and variations of the various described embodimentsprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A zeolite composite catalyst comprising amesostructure comprising at least one disordered mesophase and at leastone ordered mesophase, where the zeolite composite catalyst has asurface area defined by a Brunauer-Emmett-Teller (BET) analysis of atleast 600 m²/g and where the zeolite composite catalyst compriseszeolite beta.
 2. The zeolite composite catalyst of claim 1 where thesurface area as defined by BET is at least 700 m²/g.
 3. The zeolitecomposite catalyst of claim 1 where the zeolite composite catalyst hasan external surface area of at least 300 m²/g.
 4. The zeolite compositecatalyst of claim 1 where the zeolite composite catalyst comprises atotal pore volume of at least 0.50 cm³/g.
 5. The zeolite compositecatalyst of claim 1 where the zeolite composite catalyst compriseszeolite beta/MCM-41.
 6. The zeolite composite catalyst of claim 1 wherethe zeolite composite catalyst comprises a binder.
 7. The zeolitecomposite catalyst of claim 6 where the binder is an alumina basedbinder.
 8. The zeolite composite catalyst of claim 6 where a ratio byweight of the solid zeolite composite to binder is 3:1 to 4:1.
 9. Thezeolite composite catalyst of claim 1 where the ordered mesophase is ahexagonal mesophase.
 10. The zeolite composite catalyst of claim 1 wherethe disordered mesophase comprises a hexagonal mesophase.
 11. A methodof converting C₉₊ alkyl aromatic hydrocarbons to a product streamcomprising benzene, toluene, and xylene, the method comprising: reducinga zeolite composite catalyst comprising a mesostructure comprising atleast one disordered mesophase and at least one ordered mesophase, wherethe zeolite composite catalyst has a surface area defined by BET of atleast 600 m²/g with hydrogen gas at 400° C., where the zeolite compositecatalyst comprises zeolite beta; contacting a feed comprising C₉₊alkylaromatic hydrocarbons with the reduced composite zeolite catalystand hydrogen in a transalkylation zone of a reactor to produce atransalkylation product; stripping C₁-C₅ and lighter hydrocarbons andstripping unreacted feed from the transalkylation product; andcollecting xylenes product from the transalkylation product.
 12. Themethod of claim 11 where the transalkylation zone is at a pressurebetween 1.0 to 3.0 MPa, a temperature of 200° C. to 500° C., a spacevelocity of 1.0 to 5.0 h⁻¹, and a hydrogen to hydrocarbon ratio of 1 to4.
 13. The method of claim 11 where where the zeolite composite catalysthas an external surface area of at least 300 m²/g.
 14. The method ofclaim 11 where where the zeolite composite catalyst comprises a totalpore volume of at least 0.50 cm³/g.
 15. The method of claim 11 wherewhere the zeolite composite catalyst comprises zeolite beta/MCM-41. 16.The method of claim 11 where the zeolite composite catalyst comprises abinder.
 17. The method of claim 16 where the binder is an alumina basedbinder.
 18. The method of claim 16 where a ratio by weight of the solidzeolite composite to binder is 3:1 to 4:1.
 19. The method of claim 11where the ordered mesophase is a hexagonal mesophase.
 20. The method ofclaim 11 where the disordered mesophase comprises a hexagonal mesophase.